Quartzite

Hardness: 7 on Mohs scale. Color: Often white or light gray, but can be shades of brown, red, purple, or yellow due to impurities. Luster: Vitreous to greasy. Crystal structure: Microcrystalline to macrocrystalline granular texture. Cleavage: None (fractures conchoidally). Specific Gravity: 2.65.

Formed from sandstone that has been metamorphosed through heat and pressure, typically during regional metamorphism associated with mountain building events. The quartz grains in the sandstone recrystallize, fusing together and obliterating the original sedimentary structures. Geological Age: Varies widely, depending on the age of the original sandstone and the metamorphic event, ranging from Precambrian to relatively recent.

Industry: Used as a dimension stone for flooring, countertops, and wall cladding due to its hardness and durability. Construction: Crushed for use in road construction, railroad ballast, and as an aggregate. Jewelry/Collecting: Occasionally used in decorative items or as a collector's specimen, especially colorful varieties.

Quartzite is exceptionally durable and resistant to weathering and erosion, making it a common rock type in mountainous regions. It is often confused with marble, but unlike marble, quartzite will not effervesce with weak acids. The interlocking quartz grains give it a characteristic sugary texture and make it extremely tough.

In the field, quartzite can be identified by its hardness (scratches glass), granular texture, and conchoidal fracture. It often forms prominent ledges and ridges due to its resistance to erosion. Common locations include areas with ancient mountain ranges, such as the Appalachian Mountains in the U.S., parts of Canada, and various regions globally where strong metamorphic events have occurred. Tips for collectors: Look for fresh breaks to observe the texture and lack of cleavage. Note any color variations which can indicate mineral impurities.